I think sleep is a myth

Seriously, look at the # of books on infant/toddler/child sleep the next time you're at amazon.com or your local bookstore. If most children slept well most of the time, then those books wouldn't be there. And the majority of our society ain't cosleeping.
I do think that mainstream parents don't talk about their children's sleep problems as much, maybe because they think that they're supposed to have "trained" their child to sleep already. I also think that parents who believe in early sleep independence have trained themselves to ignore waking/noise that we would react to pretty quickly.
I think it's normal for babies to sleep next to mom and to wake frequently to eat. It's probably normal well into toddlerhood. Folks like James McKenna show research that supports this.
I think as children get older, it's personality and genetics as much as anything else. We've coslept with all our children since birth. We currently have a family bedroom with a king and a twin pushed together. DD#1 "gets" the twin to herself because she's in non-stop motion, even while asleep (one of those kicking perpendicular sleepers some others have). But she's never awake while flailing around and talking aloud. DD#1, DS, and DH are all night owls. But getting them up before 8 am - ugh! DD#2 and I would happily be in bed at 8 and up at dawn. DS and I are both lousy sleepers. It takes us forever to fall asleep, we wake frequently, we get insomnia. But DS is like a log when actually asleep. DD and DH fall asleep as soon as their heads hit the pillow.
DH and I both slept in cribs. DH was sleep trained from an early age. I was welcomed in my parents bed when I needed an adult at night. He and I have very different sleep patterns. But we've DONE the same for all our children. . .and some of them are like one of us, some like the other.